The use of solid pellets as a fuel source is known, particularly in the art of furnaces and the like. Such furnaces include a combustion space containing a combustion chamber, a transport device for the solid fuel pellets and a hopper. A convection space is provided for circulating air by means of a blower for cooling the combustion space and a flue gas blower for driving combustion of the fuel pellets. The control procedures during operation of these furnaces, required by the devices for fuel and fresh air feed due to the changing operating conditions, take place by continuous monitoring of these furnaces and automatic intervention for purposes of regulation. With this, unsupervised operation of these furnaces is possible in many cases, but the energy utilization and the operational reliability are not satisfactory.